This invention relates to a mechanism that stabilizes a boom swing-house assembly of a forestry machine by leveling the swing-house in uneven or sloping terrain.
Forestry machines, such as feller bunchers for harvesting standing trees, are well known. In one type of feller buncher, a saw head which is used to sever the tree is mounted at the end of a boom which has its other end mounted to a turntable so as to be pivotable about a lateral axis relative to the turntable. The turntable is mounted to a turntable support so as to be pivotable about a vertical axis (when the support is vertical). A carriage, which can have tracks or wheels for conveying the turntable support, has a frame to which the turntable support is mounted by a leveling mechanism. The leveling mechanism is operable to vary the position and orientation of the turntable support relative to the carriage, depending upon the slope of the terrain and the orientation of the carriage on the terrain. For example, if trees are being cut on a hillside, the machine will typically be driven onto the hillside so the trees are within reach of the boom and the leveling mechanism adjusted so as to make the axis of the turntable generally vertical. The center of gravity of the swing-house assembly; which includes the boom and the cutting head attached, the engine of the machine and the operator cab; mounted on the turntable, should be in a predetermined positioned. That position should be relative to the carriage so that the machine does not tip forward or backward when the tree is cut and its weight comes to rest on the butt plate of the head.
Such a mechanism has been made using linkages and hydraulic cylinders for moving the linkages as described in U.S. Pat. No. 4,679,803. In that mechanism, one set of links is provided forwardly and another set is provided rearwardly, and hydraulic cylinders connect the links both laterally and longitudinally to tilt the turntable relative to the carriage both about a lateral axis and a longitudinal axis. Other mechanisms for positioning and orienting the swing-house assembly relative to the carriage are also discussed in U.S. Pat. Nos. 4,679,803, and 6,173,973. The latter patent sets forth and confirms that other leveling devices for tree-harvesters require that the swing-house pivot about an axis parallel to the carriage, when the carriage is on a planar surface as shown in FIG. 6. This type of pivot action can be deleterious because the center of gravity is extremely high when a tree is being harvested.
This invention solves that problem by directing the center of gravity of the complete swing house assembly 12 away from the tip axis of the complete machine. The invention is successful because, for at least one reason, of the unique orientation of the side pivot axis 170.
In Timberjack""s Canadian patent application 2276515 claim 5 (a dependent claim), there is a reference to a similar obtuse angle being formed between the turntable major axis 34 and the side tilt axis 170. The present invention improves the angle to achieve better weight transfer and does it without the use of complicated linkages, used in Timberjack""s application, to achieve this obtuse angle.
The present invention is directed toward a stable leveling mechanism for tree harvesters. The present invention utilizes many of the same components of conventional leveling mechanisms for tree harvesters, but it alters the pivot axis of a swing-house assembly. A conventional swing-house assembly pivots about an axis parallel to the top surface of a carriage on level ground. That conventional assembly can be deleterious, therefore, applicant has altered the pivot axis of the swing-house assembly. Admittedly, merely moving the pivot axis seems simple but it is difficult. The components had to be constructed differently to obtain the desired results and simultaneously make the device stable within the working environment.